Reverse telephoto type lens prevented from the deterioration of image at the time of close shot

ABSTRACT

A reverse telephoto type lens adapted for preventing the deterioration of image at the time of close shot, comprising a front lens group having negative refractive power and a back lens group having positive refractive power, wherein the latter lens group is further divided into two positive lens groups, which are spaced by a variable air interval, and whole lens system may be shifted approximately in proportion to the variation of said interval.

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O Umted States 1 1 3,748,022 Tajima I July 24, 1973 [54] REVERSETELEPIIOTO TYPE LENS 2,785,603 3/1957 Cook 350/214 p v N E FROM THEDETERIORATION 3,512,874 5/1970 Woltche..... 350/214 3,635,546 1/1972 Mon350/214 0! IMAGE AT THE TIME OF CLOSE SHOT Inventor:

Aklra Tajlme, Kawasaki, Japan Filed: Mar. 3, 1972 Appl. No.: 231,657

Assignee:

US. Cl 350/214, 350/176, 350/255 Int. Cl. G02!) 9/64 Field of Search350/214, 215, I86

[56] Relerences Cited UNITED STATES PATENTS 2,537,912 1/1951 Reiss350/186 Primary Examiner-John K. Corbin Attorney-David Toren et al.

ABSTRACT 11 Claims, 10 Drawing Figures R5 RSRIRBRQRIO Patented July 24,1973 3,748,022

FlG.t di d 0.0| O OiOI 0.0iO 0.0! -2 O 2% Spherical Image FieldDistortion Aberration Curvature Astigmatism FlG.3a FlG.3b 0 FIG. 3%

-0.o| o 0.01 -o.o|o 0.01 -2 0 32% Spherical ImageField DistortionAberration Curvature FIG.40 FlG.4b FiG.4c

t I t 1 1M J OOI 0 ob: -o.0|oo.0| -2 0 2% Spherical ImageFieldDistortion Aberration Curvature Astigmatism REVERSE TELEPIIOTO TYPE LENSPREVENTED FROM THE DETERIORATION OF IMAGE AT THE TIME OF CLOSE SHOTBACKGROUND OF INVENTION A reverse telephoto type lens gives a long backfocus, so that it is favorable for use as a wide angle lens in asingle-lens reflex camera. However, at the time of close shot,remarkable deterioration of the image is found from the intermediateportion to the peripheral portion of a picture, and particularly it isundesirable and defective when it is applied to close shot, copying andthe like.

To prevent such a defect, there is proposed that an air interval, aportion in a lens system, is made variable, and the whole system isshifted forward, and at the same time said air interval is changed byinterlocking with the movement of said system, thus to prevent thefluctuation of the image surface, namely the variation of curvature ofimage field and astigmatism. The present invention relates to such akind of lens system.

SUMMARY OF INVENTION The present invention relates 'to a reversetelephoto type lens which is prevented from the deterioration of imageat the time of close shot.

The characteristic feature of the present invention resides in that in areverse telephoto type lens comprising a front part lens group I havingnegative refractive power and a back part lens group [I having positiverefractive power, said lens group II is further divided into twopositive lens groups II, and II, spaced by an air interval, which ismade variable, and the whole lens system is made to be shifted forwardas well as said air interval is made to be changed approximately inproportion to the amount of forward shifting at the time of close shot,thus the deterioration of image may be prevented.

Now, let the refractive power of the whole lens system be 1, that of thelens group I be that of lens group II be and the interval of principalpoint between the lens groups I and Il be D, then the condition of ismade to be satisfied, as well as said air interval is made variable, andthe whole lens system is made to be shifted forward at the time ofphotographing at infinite distance down to close shot of 0.2magnification and its air interval is made to be changed within a rangeof not more than 5 percent of the focal distance of the whole system inproportion to the amount of the forward shifting at the time of closeshot.

In said conditional inequality, the amount of 4:, 4:, D4,. 4:, denotesan angle formed by a light beam and the optical axis when the beampasses said air interval, in case the beam from an object point on theaxis of infinite distance comes in the lens system at the height of l,and let said angle be a, said conditional inequality becomes On theother hand, it is important conditions for preventing the variation ofimage field by changing the air interval at the time of close shot that(l) the variation of image field, i.e., the curvature of image field andastigmatism are especially corrected and other aberrations are almostunchanged, and (2) the focal distance and F-number of whole lens systemare not changed.

These conditions may be clearly satisfied by an interval when the beamon the axis and the optical axis are approximately parallel, i.e., by aninterval in case a==0, however, the present invention is based on theknowledge that said conditions may be also satisfied in a range of abeing 0.35 1.0.

Commonly, it is understood that as the absolute value of the angle orbecomes larger, the inclination of the beam becomes larger, and if theinterval is changed, the variation of aberration, focal distance and thelike may be caused, however, if said understanding is examined indetail, the interval having convergent light flux effects smallervariations of aberration and focal distance compared with the intervalhaving divergent light flux. The reason thereof consists in that as a ispositive and becomes larger, so the focal distance of the lens groupafter the corrected interval, i.e. of II,, becomes longer, and in caseof or-l the focal distance of II, becomes infinity, thus the focaldistance of whole system remains utterly unchanged.

Therefore, as is the case of the present invention, if the back group IIof positive refraction power to the front group I of negative refractionpower is divided into two groups II II, of positive refraction power andmake their refraction power is d, and interval of principal point D tohave the relation of 0.35 4,, d, D,5 l, the correction of thecharacteristics of image field of whole lens system at the time of closeshot becomes possible by changing the air interval between two lensgroups of the back group, and if the lower limit is exceeded, saidcorrection becomes difficult, while if the upper limit is over, bychanging the corrected interval, remarkable increase of sphericalaberration will result.

In the present invention, the range of magnification is limited up to0.2 times and the corrected air interval is limited within 5 percent ofthe focal distance of the whole lens system, the reason thereof will beexplained as follows.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 shows a construction of lensaccording to the present invention as an embodiment thereof.

FIGS. 2a-2c show an aberration diagram in case of infinite distancephotographing in said embodiment.

FIGS. 30-30 show an aberration diagram in case of close shot with themagnification of 0.l l8 by shifting forward of the whole lens system asusual, in said embodiment. v

FIGS. 8-46 show an aberration diagram in case of close shot bycorrecting the variable lens interval.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Numerical examples of theembodiment according to the present invention will be shown as follows:

R radius of curvature of each refraction surface, in order of numerals.

d thickness of each lens on axis or air interval, in order of numerals YN refractive index of each lens, in order of numerals.

V Abbes number of each lens, in order of numerals.

d variable Variable air interval D is 01541 at the object distance of wand is 0.1345 at the time of close shot with a magnification of 0.1 18

N, 1.7737 V, 49.2 R 3.877

d 0.0905 N, 1.76182 V, 26.5 R -1 170 d1: R 13.96

d 0.1226 N, 1.80518 V, 25.4 R", i

d 0.0029 N 1.7737 V; 49.2 R, 1.970

d 0.0827 N 1.8061 V, 40.8 R 3.278 In the above-mentioned embodiment, 45,=0.6575, 1b, 1.1549, D 0.4762 4:, 4),

D z I FIG. 2 shows an aberration diagram in case of infinite distancephotographing in said embodiment and each aberration is successfullycorrected, however, if, under this condition of air interval D as it isand by shifting whole lens system as usual, the close shot is effected,its condition of aberration becomes as shown in FIG. 3, particularly theastigmatism and the curvature of image field will be remarkablydeteriorated. In this case, if the air interval D is changed asabove-mentioned simultaneously with the shifting of whole lens system,then the condition of aberration becomes as shown in FIG. 4,

6 thus the astigmatlsm and the curvature of 1mage field will not bedeteriorated.

What is claimed is:

l. A reverse telephoto lens, comprising a front lens group I having anegative refractive power and a back lens group II having a positiverefractive power, said lens group 11 being divided into two positivelens groups 11 l and 11 spaced from each other by an air interval, saidair interval being variable, said two groups together being shiftablealong the axis, the distance between the lens groups Il,'and 11, beingvariable during shift of said groups so as to change the air intervalapproximately in proportion to the amount of shift so as to preventdeterioration of the image, said groups having a plurality of individuallenses, the following conditions being satisfied for the lenses:

d, 0.0028 N, 1.697 v, 48.5 R, 1.816

.1, 0.3462 R 1.51633 v, 64.0 R, 0.9749 d, 0.0972 R, 1.0s2

d, 0.0029 N, 1.70154 V, 41.1 R-, 1.072

a, 0.0419 N, =1.7 v, 48.0 R, 1.333

d variable* Variable air interval D is 0.1541 at the object distance ofw and is 0.1345 at the time of close shot with a magnification of 0.118N, [.7737 V 49.2

R! d 0.0905 N. 1.76182 V, 26.5 R13 l d 3 R I396 d 0.1226 N l.805l8 V-,25.4 R 0.6989

(1 0.0029 N 1.7737 V; 49.2 R,, 1.970 d e N9 V9 R11 f= 1 1 2 20.1 64 backfocus 1.1066 wherein,

R radius of curvature of each refraction surface, in

order of numerals. d thickness of each lens on axis or air interval, in

order of numerals. N refractive index of each lens, in order ofnumerals. V Abbes number of each lens, in order of numerals. 2. A lensas in claim I, wherein the groups are shifted forward for close-up shotsand the air interval is changed approximately in proportion to theamount of forward shift for a close-up shot.

3. A lens system, comprising front lens means having a negativerefractive power, back lens means having a positive refractive power,said front lens means and said'back lens means togther forming aninverted telephoto type lens, said back lens means having two positivelens groups spaced from each other by an air interval, said lens groupsbeing movable relative to each other so as to vary the air interval,said first lens means and said second lens means being shiftable alongthe axis for focusing, said groups being movable relative to each otherso as to change the interval approximately in proportion to the shift ofsaid first and second lens means for at least a portion of the movementrange of said lens means and thereby prevent deterioration of an imagebeing formed.

4. A system as in claim 3, wherein said first and second lens means maybe moved forward together for focusing on a close-up object, said groupsbeing movable relative to each other so as to change the air intervalproportional to the shift of said lens means in the range of focusingfor a close-up shot.

5. A lens system as in claim 3, wherein said front lens means has aforward element, said forward element having a forward surface facing anobject whose image is to be formed, said forward surface being concave.

6. A system as in claim 5, wherein said first and second lens means maybe moved forward together for focusing on a close-up object, said groupsbeing movable relative to each other so as to change the air intervalproportional to the shift of said lens means in the range of focusingfor a close-up shot.

7. A system as in claim 3, wherein said first and second lens meanssatisfy a condition when the refractive power of said front lens meansand power of said back lens means is l00,, and the interval between theprincipal point of said front lens means the refractive power of saidfront lens means and said back lens means together are l and ltherefractive power of the front lens means is 4) the refractive power ofsaid back lens means being (1),, and the interval between the principalpoint of said front lens means and l of said lens groups is D.

10. A system as in claim 3, wherein said first and second lens meanssatisfy a condition,

when the refractive power of said front lens means and said back le'nsmeans together are l and the refractive power of the front lens means is4),, the refractive power of said back lens means being 4: and theinterval between the principal point of said front lens means and l ofsaid lens groups is D.

11. A system as in claim 10, wherein when the magnification of the frontlens means and the back lens means together is less than 0.2 thecorrected air interval is less than 5 percent of the focal distance ofsaid inverted telephoto lens together.

# i t i t

1. A reverse telephoto lens, comprising a front lens group I having anegative refractive power and a back lens group II having a positiverefractive power, said lens group II being divided into two positivelens groups II 1 and II 2 spaced from each other by an air interval,said air interval being variable, said two groups together beingshiftable along the axis, the distance between the lens groups II1 andII2 being variable during shift of said groups so as to change the airinterval approximately in proportion to the amount of shift so as toprevent deterioration of the image, said groups having a plurality ofindividual lenses, the following conditions being satisfied for thelenses: R1 -5.776 d1 0.0975 R2 -3.231 d2 0.0028 N1 1.697 V1 48.5 R31.816 d3 0.0418 R4 0.4944 d4 0.3462 N2 1.51633 V2 64.0 R5 -0.9749 d50.0972 R6 -1.082 d6 0.0029 N2 1.70154 V3 41.1 R7 1.072 d7 0.0960 R815.83 d8 0.0419 N4 1.7 V4 48.0 R9 1.333 d9 0.2890 R10 124.1 d10variable* Variable air interval D10 is 0.1541 at the object distance ofinfinity and is 0.1345 at the time of close shot with a magnification of0.118 N5 1.7737 V5 49.2 R11 -3.877 d11 0.0279 R12 0.8554 d12 0.0905 N61.76182 V6 26.5 R13 -1.170 d13 0.028 R14 13.96 d14 0.1226 N7 1.80518 V725.4 R15 -0.6989 d15 0.0029 N8 1.7737 V8 49.2 R16 1.970 d16 0.0827 N91.8061 V9 40.8 R17 -3.278 f 1 1 : 2 2 omega 64* back focus 1.1066wherein, R : radius of curvature of each refraction surface, in order ofnumerals. d : thickness of each lens on axis or air interval, in orderof numerals. N : refractive index of each lens, in order of numerals. V: Abbe''s number of each lens, in order of numerals.
 2. A lens as inclaim 1, wherein the groups are shifted forward for close-up shots andthe air interval is changed approximately in proportion to the amount offorward shift for a close-up shot.
 3. A lens system, comprising frontlens means having a negative refractive power, back lens means having apositive refractive power, said front lens means and said back lensmeans togther forming an inverted telephoto type lens, said back lensmeans having two positive lens groups spaced from each other by an airinterval, said lens groups being movable relative to each other so as tovary the air interval, said first lens means and said second lens meansbeing shiftable along the axis for focusing, said groups being movablerelative to each other so as to change the interval approximately inproportion to the shift of said first and second lens means for at leasta portion of the movement range of said lens means and thereby preventdeterioration of an image being formed.
 4. A system as in claim 3,wherein said first and second lens means may be moved forward togetherfor focusing on a close-up object, said groups being movable relative toeach other so as to change the air interval proportional to the shift ofsaid lens means in the range of focusing for a close-up shot.
 5. A lenssystem as in claim 3, wherein said front lens means has a forwardelement, said forward element having a forward surface facing an objectwhose image is to be formed, said forward surface being concave.
 6. Asystem as in claim 5, wherein said first and second lens means may bemoved forward together for focusing on a close-up object, said groupsbeing movable relative to each other so as to change the air intervalproportional to the shift of said lens means in the range of focusingfor a close-up shot.
 7. A system as in claim 3, wherein said first andsecond lens means satisfy a condition 0.35< phi 1+ phi 2-D1 phi 1 phi2<1.0 when the refractive power of said front lens means and said backlens means together are 1 and the refractive power of the front lensmeans is phi 1, the refractive power of said back lens means is 1002,and the interval between the principal point of said front lens meansand 1 of said lens groups is D.
 8. A lens system as in claim 3, whereinwhen the magnification of the front lens means and the back lens meanstogether is less than 0.2 the corrected air interval is less than 5percent of the focal distance of said inverted telephoto lens together.9. A system as in claim 8, wherein said first and second lens meanssatisfy a condition 0.35< phi 1+ phi 2-D1 phi 1 phi 2<1.0 the refractivepower of said front lens means and said back lens means together are 1and lthe refractive power of the front lens means is phi 1, therefractive power of said back lens means being phi 2, and the intervalbetween the principal point of said front lens means and 1 of said lensgroups is D.
 10. A system as in claim 3, wherein said first and secondlens means satisfy a condition, 0.35< phi 1+ phi 2-D phi 1 phi 2<1.0when the refractive power of said front lens means and said back lensmeans together are 1 and the refractive power of the front lens means isphi 1, the refractive power of said back lens means being phi 2, and theinterval between the principal point of said front lens means and 1 ofsaid lens groups is D.
 11. A system as in claim 10, wherein when themagnification of the front lens means and the back lens means togetheris less than 0.2 the corrected air interval is less than 5 percent ofthe focal distance of said inverted telephoto lens together.